Impact of Low Blood Lead Concentrations on IQ and School Performance in Chinese Children

Objectives: Examine the relationships between blood lead concentrations and children's intelligence quotient (IQ) and school performance. Participants and Methods: Participants were 1341 children (738 boys and 603 girls) from Jintan, China. Blood lead concentrations were measured when children were 3-5 years old. IQ was assessed using the Chinese version and norms of the Wechsler Preschool and Primary Scale of Intelligence - Revised when children were 6 years old. School performance was assessed by standardized city tests on 3 major subjects (Chinese, Math, and English [as a foreign language]) when children were age 8-10 years. Results: Mean blood lead concentration was 6.43 mu g/dL (SD = 2.64). For blood lead concentrations, 7.8% of children (n = 105) had >= 10.0 mu g/dL, 13.8% (n = 185) had 8.0 to <10.0 mu g/dL, and 78.4% (n = 1051) had <8.0 mu g/dL. Compared to children with blood lead concentrations <8 mu g/dL, those with blood lead concentrations >= 8 mu g/dL scored 2-3 points lower in IQ and 5-6 points lower in school tests. There were no significant differences in IQ or school tests between children with blood lead concentrations groups 8-10 and >= 10 mu g/dL. After adjustment for child and family characteristics and IQ, blood lead concentrations >= 10 mu g/dL vs <8 mu g/dL at ages 3-5 years was associated with reduced scores on school tests at age 8-10 years (Chinese, beta = -3.54, 95%CI = -6.46, -0.63; Math, beta = -4.63, 95%CI = -7.86, -1.40; English, beta = -4.66, 95%CI = -8.09, -1.23). IQ partially mediated the relationship between elevated blood lead concentrations and later school performance. Conclusions: Findings support that blood lead concentrations in early childhood, even <10 mu g/dL, have a long-term negative impact on cognitive development. The association between blood lead concentrations 8-10 mu g/dL and cognitive development needs further study in Chinese children and children from other developing countries.